Exhaust silencer



July 9, 1957 J. c. FISCHER, JR

EXHAUST SILENCER 2 Sheets-Sheet 1 Filed Jan. 11, 1954 INVENTOR. JOHN c. FISCHER, JR.

B $1 m & 56m:

ATTORNEY IN FALI FQR APPLlcAMT July 9, 1957 .1. c. FISCHER, JR

EXHAUST SILENCER 2 Sheets-Sheet 2 Filed Jan. 11, 1954 INVENTOR. JOHN c. nscflcmm.

162101 & K/nax ATTQRNEY IN FACT FOR APILI ANT United States Patent 2,798,569 EXHAUST SILENCER John C. Fischer, Jr., San Diego, Calif. Application January 11, 1954, Serial No. 403,271 9 Claims. (Cl. 181-42) The present invention relates generally to mufilers and more particularly to a silencer for the exhausts of internal combustion engines.

The primary object of this invention is to provide a silencer having a rectilinear flow to reduce back pressure and having exceptional sound absorbing qualities, effective in dampening vibrations throughout a wide frequency range.

Another object of this invention is to provide a silencer having resonance chambers of a novel design.

Another object of this invention is to provide a silencer in which the resonance chambers are adjustable axially of the silencer, while the device is in use so that the resonant frequency of the silencer as a unit may be adjusted for maximum efliciency with reference to the particular engine connected thereto.

Another object of this invention is to provide a silencer having an absorbent filling of heat and corrosion resistant material, thus enabling the silencer to be used at extremely high temperatures.

Another object of this invention is to provide a silencer in which the sound absorbing material is substantially resilient, so that packing or shifting of the filling is prevented, even under extreme vibration.

Another object of this invention is to provide a silencer which is inexpensive and practicable to manufacture.

Finally, it is an object to provide a silencer of the aforementioned character which is simple, safe and convenient to operate, and which will give generally eflicient and durable service.

With these and other objects definitely in view, this invention consists in the novel construction, combination and arrangement of elements and portions as will be hereinafter fully described in the specification, particularly pointed out in the claims and illustrated in the draw ing which forms a material part of this disclosure and wherein similar characters of reference indicates similar or identical elements and portions throughout the specification and throughout the views of the drawing, and in which:

Fig. 1 is a perspective view, silencer.

Fig. 2 is a longitudinal sectional view of the silencer.

Fig. 3 is a sectional view taken on the line 3-3 of Fig. 2.

Fig. 4 is a longitudinal sectional view, similar to Fig. 2, of a modified form of the silencer having adjust-able resonance chambers.

Fig. 5 is an end elevation view of the silencer shown in Fig. 4.

Fig. 6 is a sectional view taken on the line 6-6 of Fig. 4-.

Fig. 7 is a diagrammatic side elevation view of the silencer attached to an aircraft jet engine.

Referring now to the drawing, and in particular to Figs. 1-3, the silencer comprises an outer imperforate canister 10 constituting the outer body or shell of the silencer, having an inner concentric tube 12, the projecting ends of said tube constituting the exhaust pipe connections 14. Within the canister 10 and surrounding the tube 12 are a plurality of resonance chambers 16, the remainder of the annulus between said canister and said tube containpartially cut away, of the ing the sound absorbent filling 18. The ends of the canister 10 are closed by end plates 20 in sealed contact therewith and with the tube 12. The portion of the tube 12 between the end plates 20 is provided with a plurality of perforations 22.

The resonance chambers 16 are formed by spools 24, each comprising a cylindrical portion 26 having a flange 23 at each end thereof. The cylindrical portions 26 are provided with perforations 30. The spools 24 are a reasonably close fit within the canister 10 and are arranged at spaced intervals. The filling 18 serves to hold the spools 24 in place.

The pipe connections 14 have slots 32 to facilitate a tight joint with the exhaust pipe portions 34 and 36, shown dotted in Fig. 2.

The silencer is constructed of corrosion and heat resistant metal of a suitable type commonly used in exhaust systems. The filling 18 is also of corrosion and heat resistant material, a particularly suitable material being vermiculite or the like. Vermiculite is a porous granular material containing a large number of natural air cells, and is of a substantially resilient nature. This resiliency enables the filling to absorb shocks and vibration, so that packing and uneven distribution of the filling are prevented. The particles of filling are, of course, larger than the perforations 22 and to prevent loss of the material. The extremely porous nature of vermiculite ensures the eificient deadening of sound from engine exhausts of many types.

The resonance chambers 16 are most eificient when the silencer is used on the relatively low frequency exhausts of reciprocating engines. The size of the spools 24 and the number of spools used may be calculated for particular exhaust installations so that the silencer effectively dampens vibrations set up by the exhaust, the resonant frequency of the silencer being chosen so as to be well removed from the major frequency or the vibration characteristic of the exhaust.

In order to adapt the silencer for use with various types of engines having different vibration frequencies, provi sion is made for longitudinal adjustment of the resonance chambers 16 in the silencer. The end plates 20 are each fitted with a plurality of removable screw plugs 37 which, when removed, facilitate the insertion of a rod or other suitable tool to move the resonance chambers 16, so that the resonant frequency of the silencer may be varied as required. The vermiculite filling 18 offers little re sistance to movement of the resonance chambers 16 due to its great resiliency.

The silencer is equally suitable for use with high frequency exhausts and, when manufactured in sufiiciently large sizes, may be used to silence jet engines, particularly when the jet engines are being tested near a populated area as is often the case. A form of the silencer suitable for use with jet engines is illustrated in Figs. 47. The silencer comprises an outer canister 38 having end plates 40. Within the canister 10 is an inner concentric tube 42, the ends of which extend through the end plates 40 and are sealed thereto, the extended ends comprising an inlet 44 and an outlet 46. Within the canister 38 and surrounding the tube 42 are a plurality of resonance chambers 48 each comprising a cylindrical portion 50 having a flange 52 at each end thereof. The cylindrical portion 50 is provided with perforations 54 and the tube 42 has similar perforations 56. The annulus between the canister 38 and the tube 42 is filled with sound absorbent filling 18, which is shown in part only for clarity. The construction thus far is substantially similar to that previously described. Secured to the inside of the canister 38, and extending longitudinally therein, are diametrically opposed guide rails 58. The flanges 52 of the resonance chambers are provided with notches 60 to clear the guide rails 58. Secured to the flanges 52 adjacent the notches 60 are brackets 62 each carrying a roller 64, said rollers bearing in the guide rails 58. The resonance chambers .48 are thus longitudinally movable and. are adjusted by means of screwed rods 66 threaded through the flanges 52. The screwed rods 66, of which three are shown asan example, are equally spaced around the flanges 52 and extend through the end plates 40. The ends of the screwed rods 66 are fitted with sprockets 68 and are interconnected by drive chains 70 to ensure synchronization of the rods and to prevent jamming of the resonance chambers 48 while being adjusted. One of the screwed rods 66 at each end is also fitted with a hand wheel 72 so that the resonance chambers may be adjusted manually, although power operated means may be used if desired. The resilient nature of the vermiculite used as the filling 18 permits limited longitudinal adjustment of the resonance chambers 48. To facilitate large adjustments of the resonance chambers 48, the filling 18 may be removed from the canister 38 by a suction device or other suitable means, and replaced when the adjustments are completed.

This particular silencer is suitable for use with jet engines which are often tested while attached to suitable stands or test beds. As shown in Fig. 7, a jet engine 74 is mounted with its exhaust in the inlet 44 of the silencer. The mounting stand for the jet engine and the necessary support structure for the silencer are omitted for clarity. The operating speeds of jet engines, and consequently their sound frequencies, vary with different types of engines. By using a silencer having adjustable resonance chambers as shown, the silencer may be adjusted while the jet engine is actually in operation to obtain the maximum silencing effect.

The high fusion temperature of vermiculite (about 2500 F.) enables the silencer to be welded together after filling, with a resultant reduction in cost of manufacture. The loss of vermiculite in the vicinity of the welds due to excess temperatures would be negligible. 7

The operation of this invention will be clearly comprehended from a consideration of the foregoing description of the mechanical details thereof, taken in connection with the drawing and the above recited objects. It will be obvious that all said objects are amply achieved by this invention.

Further description would appear to be unnecessary.

It is understood that minor variation from the form of the invention disclosed herein may be made without departure from the spirit and scope of the invention and that the specification and drawing are to be considered as merely illustrative rather than limiting.

I claim:

1. A silencer for connection to an engine exhaust, comprising a canister, a perforated tube in said canister, means discrete from said canister to define therewith a resonance chamber spaced from and surrounding said tube, said means including a perforated, hollow cylindrical portion disposed between said tube and canister, a filling of granuar, porous sound absorbent material between said tube and said canister, said resonance chamber communicating with said tube only through said absorbent material.

2. A silencer for connection to an engine exhaust, comprising a canister, a perforated tube in said canister, means discrete from said canister and cooperating with adjacent portions of said canister to define at least one resonance chamber radially spaced from and surrounding said tube and within said canister, a filling of granular, porous sound absorbent material between said tube and said canister, said resonance chamber communicating with said tube only through said absorbent material.

3. A silencer comprising an elongated canister, a perforated tube disposed longitudinally in said canister, said tube having integral exhaust pipe connection portions extending from said canister, at least one spool in said canister, each spool comprising a perforated cylindrical portion having flanges at the ends thereof, said spool and the adjacent portion of the canister defining a resonance chamber consisting of the annulus between said cylindrical portion and said canister enclosed by said flanges, said cylindrical portion and said resonance chamber being spaced radially from said tube, and a filling of granular, porous sound absorbing material between said tube and said canister and between said tube and said resonance chamber.

4. A silencer according to claim 1 wherein said filling comprises vermiculite.

5. A silencer comprising a canister having end plates therein, a perforated tube longitudinally mounted in said canister, said tube having integral exhaust pipe connection portions extending through said end plates, at least one spool in said canister, each spool comprising a perforated cylindrical portion radially spaced from said tube and having flanges at the ends thereof, said flanges being in contact with said canister, said spool and the adjacent portion of the canister defining a resonance chamber consisting of the annulus between said cylindrical portion and said canister enclosed by said flanges, said cylindrical portion and said resonance chamber being spaced radially from said tube and a filling of vermiculite between said tube and said canister and between said tube and said cylindrical portion.

6. A silencer comprising a canister having end plates therein, a perforated tube disposed longitudinally in said canister, said tube having integral exhaust pipe connection portions extending through said end plates, at least one resonance chamber surrounding said tube, said resonance chamber being axially shiftable in said canister, said end plates being apertured to accommodate means for shifting said resonance chamber, and a filling of granular porous material disposed exteriorly of said resonance chamber between said tube and said canister.

7. A silencer comprising a canister having end plates therein, a perforated tube disposed longitudinally in said canister, said tube having integral exhaust pipe connection portions extending through said end plates, at least one resonance chamber surrounding said tube, said resonance chamber being axially shiftable in said canister, externally accessible screw adjusting means operatively connected to said resonance chamber, and a filling of granular, porous material between said tube and said canister.

8. A silencer comprising a canister having end plates therein, a perforated tube disposed longitudinally in said canister, said tube having integral exhaust pipe connection portions extending through said end plates, longitudinal guide rails in said canister, a plurality of resonance chambers surrounding said tube and slidable on said guide rails, externally accessible screw adjusting means operatively connected to said resonance chambers, and a filling of granular, porous sound absorbing material between said tube and said canister.

9. A silencer comprising a cani er having end plates therein, a perforated tube disposed longitudinally in said canister, said tube having integral exhaust pipe connection portions extending through said end plates, longitudinal guide rails in said canister, a plurality of resonance chambers surrounding said tube and slidable on said guide rails, externally accessible screwed rods engaging said resonance chambers for longitudinal adjustment thereof, driving means interconnecting said screwed rods, and a filling of granular, porous material between said tube and said canister.

References Cited in the file of this patent UNITED STATES PATENTS 1,173,687 Thompson Feb. 29, 1916 1,912,544 Slidell June 6, 1933 1,975,861 Oldberg Oct. 9, 1934 2,043,731 Bourne June 9, 1936 2,685,936 Brenneman et al Aug. 10, 1954 

